1. Field of the Invention
The present invention relates to a device and method of measuring a mass of a substance such as an odor molecule.
2. Related Art Statement
Japanese Patent No. 3003811 discloses a quartz vibrator microbalance device for measuring a minute change of a mass on the vibrator, based on a change of resonance frequency of the quartz vibrator. Japanese Patent Publication No. 5-346384A and Japanese Patent No. 3139 562 disclose a method of measuring a mass of an odor molecule. That is, an electrode and an organic adsorption film are provided on the surface of a quartz vibrator, in which a vibration is excited at a specific frequency. Odorant molecules adsorbed onto the organic adsorption film result in a change of the frequency of the vibrator. A mass of the odor molecules is calculated based on the change of frequency of the vibrator.
According to the prior arts, thickness-shear vibration of a so-called AT cut quartz vibrator is utilized. For example, as schematically shown in FIGS. 9(a) and (b), a measuring device 12 has a quartz vibrator 2 substantially having a shape of a disk. Electrodes 13A and 13B are formed on surfaces 2a and 2b of the quartz vibrator 2, respectively. A thickness-shear vibration is excited in the quartz vibrator 2. In the vibration, the following equations are satisfied between a change of mass and change of frequency. It is thus possible to calculate Δm (change of mass) by measuring Δf (change of frequency of basic vibration).Δf=−2Δmf2/A(μρ)1/2
Δf: change of frequency of basic vibration
f: frequency of basic vibration
Δm: change of mass
A: area of electrode
μ: elastic modulus of torsion of quartz=1011 dyn/cm2 
ρ: density of quartz=2.65 g/cm3 